Fluorination is an effective strategy to fine-tune the electronic structure and optoelectronic response of organic semiconductors by modulating frontier orbital energies, intramolecular charge transfer, and solid-state/solution interactions. Herein, four fluorinated derivatives (DFBT1-DFBT4) were rationally designed by introducing fluorine substituents on the central core of a reference molecule (DFBT-PMTP), and their properties were evaluated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Relative to the DFBT-PMTP (HOMO = -4.91 eV; LUMO = -1.87 eV), fluorination systematically stabilizes the LUMO (down to -2.10 eV) and increases electron affinity (0.94 to 1.04 eV), while moderately tuning the HOMO (-4.90 to -5.01 eV) and narrowing the bandgap (2.83 to 2.98 eV). TD-DFT predicts a modest red-shift in absorption, with <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:{{\uplambda\:}}_{\text{m}\text{a}\text{x}}\)</EquationSource> </InlineEquation> spanning 389–409 nm in gas phase and 399–419 nm in the chlorobenzene, accompanied by intense electronic transitions (high oscillator strengths). Solvation free energies indicate favorable stabilization in chlorobenzene and dimethyl sulfoxide (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\:{\Delta\:}{\text{G}}_{\text{s}\text{o}\text{l}}\)</EquationSource> </InlineEquation> ≈ -8.18 to -8.86 and − 10.87 to -11.66, respectively), consistent with moderate hydrophobicity (LogP ≈ 2.72–2.93). Charge-transport descriptors improve upon fluorination, with reduced internal reorganization energies (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\:{\lambda\:}_{h}\)</EquationSource> </InlineEquation> down to 0.5308 eV for DFBT4; <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\:{\lambda\:}_{e}\)</EquationSource> </InlineEquation> down to 0.4756 eV for DFBT3), and enhanced Marcus-type hole transfer rates relative to DFBT-PMTP (up to 3.85 × 1012 s− 1 for DFBT2). Overall, fluorination offers a practical handle to balance energy-level tuning, optical response, solubility tendency, and charge-transport propensity; notably, DFBT2 is highlighted for the highest predicted hole-transfer kinetics, while DFBT4 (and DFBT3) stand out for minimized reorganization losses, together identifying the most promising candidates for hole-transport layers in perovskite solar cells.

Theoretical Study on the Optoelectronics and Charge Transport Properties of Difluoro Benzothiadiazole-based Hole Transport Materials for Perovskite Solar Cells

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2026年2月19日

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Sayyar Ali Shah,
Rani Sayyar,
Xiaomei Zou,
Shah Faisal Mohammad,
Tazeem Fatima,
Nabi Ullah,
Ouyang Chun

摘要

Fluorination is an effective strategy to fine-tune the electronic structure and optoelectronic response of organic semiconductors by modulating frontier orbital energies, intramolecular charge transfer, and solid-state/solution interactions. Herein, four fluorinated derivatives (DFBT1-DFBT4) were rationally designed by introducing fluorine substituents on the central core of a reference molecule (DFBT-PMTP), and their properties were evaluated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Relative to the DFBT-PMTP (HOMO = -4.91 eV; LUMO = -1.87 eV), fluorination systematically stabilizes the LUMO (down to -2.10 eV) and increases electron affinity (0.94 to 1.04 eV), while moderately tuning the HOMO (-4.90 to -5.01 eV) and narrowing the bandgap (2.83 to 2.98 eV). TD-DFT predicts a modest red-shift in absorption, with \(\:{{\uplambda\:}}_{\text{m}\text{a}\text{x}}\) spanning 389–409 nm in gas phase and 399–419 nm in the chlorobenzene, accompanied by intense electronic transitions (high oscillator strengths). Solvation free energies indicate favorable stabilization in chlorobenzene and dimethyl sulfoxide ( \(\:{\Delta\:}{\text{G}}_{\text{s}\text{o}\text{l}}\) ≈ -8.18 to -8.86 and − 10.87 to -11.66, respectively), consistent with moderate hydrophobicity (LogP ≈ 2.72–2.93). Charge-transport descriptors improve upon fluorination, with reduced internal reorganization energies ( \(\:{\lambda\:}_{h}\) down to 0.5308 eV for DFBT4; \(\:{\lambda\:}_{e}\) down to 0.4756 eV for DFBT3), and enhanced Marcus-type hole transfer rates relative to DFBT-PMTP (up to 3.85 × 10¹² s^− 1 for DFBT2). Overall, fluorination offers a practical handle to balance energy-level tuning, optical response, solubility tendency, and charge-transport propensity; notably, DFBT2 is highlighted for the highest predicted hole-transfer kinetics, while DFBT4 (and DFBT3) stand out for minimized reorganization losses, together identifying the most promising candidates for hole-transport layers in perovskite solar cells.